Rechargeable electrochemical energy storage device

ABSTRACT

A rechargeable energy storage device is disclosed. In at least one embodiment the energy storage device includes an air electrode providing an electrochemical process comprising reduction and evolution of oxygen and a capacitive electrode enables an electrode process consisting of non-faradic reactions based on ion absorption/desorption and/or faradic reactions. This rechargeable energy storage device is a hybrid system of fuel cells and ultra-capacitors, pseudo-capacitors, and/or secondary batteries.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a Continuation of U.S. application Ser. No.12/960,002, filed Dec. 3, 2010 in the U.S. Patent and Trademark Office,the disclosure of which is incorporated herein by reference in itsentirety.

FIELD OF INVENTION

This invention relates to energy storage devices. More specifically, thepresent invention relates to a type of rechargeable energy storagedevices that have both air electrodes and capacitive electrodes forenergy storage.

BACKGROUND OF THE INVENTION

Batteries and capacitors represent two most important systems for energystorage, with applications in electronics, electric vehicles, telephonecommunication systems, power supplies, and many other applications.

A battery is used to store electricity by converting electric energyinto chemical energy during charging and converting chemical energy backinto electric energy during discharging. The energy is stored throughchemical reactions, which are often associated with the change ofoxidation states of active metal species (faradic reactions).Electro-active materials are often the active component in batteriessince they can provide redox reactions for energy storage. Because ofthe high theoretical energy storage capacities, metals have been pursuedas the negative electrode materials for high energy batteries. Batteriesbased on metals, however, generally have poor cycling stabilities duringthe charge/discharge process. The instability normally comes from theirreversible metal dissolution/deposition process. Metals may dissolveinto metal ions during the discharge process in those batteries. Forexample, in a zinc-nickel oxide battery, metallic zinc dissolves as zincions during discharging and deposit back as metallic zinc from zinc ionsduring charging. This dissolution/deposition process is not repeatableas zinc tends to form dendrites in solution instead of depositing backonto the current collector as the original metallic film. Similarproblems have been encountered in lithium batteries, where the metalliclithium dissolves as lithium ions during discharging and the lithiumions deposit as metallic lithium during charging. Capacitive materialswill be more stable if they can maintain their solid morphology duringthe charge/discharge process. For example, in lithium ion batteries,metals such as tin may form alloys with lithium ions during charging andthe alloys release lithium ions back into the electrolyte duringdischarging. During the charge/discharge cycling process, thenon-lithium metals experience volume expansion/contraction because theinsertion/extraction of lithium ions. However, since the solidmorphologies are maintained for these metals, the cycling stability hasbeen greatly improved for tin-based lithium ion batteries as compared tolithium batteries. The typical charge/discharge cycling number is onlyat most tens of cycles for metallic lithium-based batteries, while thetypical cycling number for lithium ion batteries with tin negativeelectrodes can be hundreds of cycles. These non-dissolvingelectro-active materials, however, may still have limitedcharge/discharge cycling stability mainly because of the volume changeassociated with the faradic reactions. The lithium ion insertion andextraction processes will cause the volume of the non-dissolvingelectro-active material to expand and to contract, which will disruptthe original compact structure of the electrode film resulting in theloss of electric connections among the electro-active particles, whichin turn results in the fading of capacity during the charge/dischargecycling. Unlike the dissolution/deposition process, instability from thevolume expansion/contraction process can be limited by controlling thematerial architecture in the electrode. For example, the stability canbe improved greatly by coating the electro-active material onto a stablecarbonaceous material, so that the electric connections to theelectro-active material can be maintained during the volumeexpansion/contraction process.

As another type of energy storage devices, electrochemical capacitorsstore electric energy mainly through the highly reversible electricstatic interactions (double-layer adsorption/desorption or non-faradicreactions). Since there is negligible physical state change of theelectrode material during the charge/discharge process, anelectrochemical capacitor can have excellent cycling stability up to20,000,000 cycles. Electrochemical capacitors, however, are limited inenergy densities. In a capacitor, the amount of charge that can bestored is directly proportional to the available electrode/electrolyteinterfaces for ions adsorption/desorption. The maximum energy densitythat can be stored therefore is limited by the surface area of theelectrode material. The energy density can be improved by using anasymmetric structure, where one electrode consists of an electro-inertporous carbonaceous material and the other electrode consists of anelectro-active material. The incorporation of an electro-active materialcan greatly increase the energy density of the device by using lesstotal electrode materials since the electro-active material can have atleast several times larger capacity than an electro-inert material. Acapacitor's capacitance can be calculated as1/(m_(T)C_(T))=1/(m_(n)C_(n))+1/(m_(p)C_(p)), where C_(T) is thedevice's specific capacitance, C_(n) is the specific capacitance for thenegative electrode, C_(p) is the specific capacitance for the positiveelectrode, m_(T) is the total weight of the two electrode materials,m_(n) is the weight for negative electrode weight, and m_(p) is theweight for positive electrode weight. For a symmetric double-layercapacitor, C_(n) equals C_(p). To maximize the value of C_(T), it isnecessary to make m_(n)C_(n) and m_(P)C_(P) to be the same valueresulting in a mass ratio of 1 of m_(n)/m_(p). C_(T) therefore is ¼ ofC_(n) or C_(p). In an asymmetric capacitor, if C_(p) (electro-activematerial) is far larger than C_(n) (porous carbon), m_(p) could be muchsmaller than m_(n). m_(T) therefore will be close to the weight of m_(n)yielding a much larger value of C_(T). J. P. Zheng calculated thetheoretical limitation of energy densities for the two systems. Themaximum energy density is 7.16 Wh/kg for an activated carbon/activatedcarbon symmetric capacitor, while the value reaches 50.35 Wh/kg for anactivated carbon/Ni(OH)₂ asymmetric capacitor with aqueous electrolyte.Regardless of the advantage of electro-active materials, chargecapacities of these materials, however, are still limited (for exampletheoretical capacity for NiOOH is 292 mAh/g). Higher energy density canbe expected if the positive electrode can store much more energy so thatthe electrode weight can be further reduced.

As a hybrid system of batteries and fuel cells, metal-air batteries havebeen a focus as the energy storage devices with high energy densities.In this system, a pure metal such as lithium and zinc is used as fuel togenerate electrons as the negative electrode. Oxygen from air is used asthe oxidant at the positive electrode side. During discharging, themetal is oxidized at the negative electrode, while oxygen is reduced bya catalyst at the positive electrode (air electrode). During charging,the oxidized metal ions are reduced into metal particles, while oxygenis generated by using an oxygen evolution catalyst at the positiveelectrode. Since oxygen can be fed from air, the theoretical energycapacity at the air electrode is unlimited large. The theoretical energydensity of this system is determined by the energy capacity of the metaland the operating voltage window.

This system, however, is generally limited by its poor charge/dischargecycling stability, which is mainly caused by the instability of thenegative electrode during cycling. The prior art air batteries have beenlimited into either using metals as negative electrode materials inaqueous alkaline electrolyte or metallic lithium as the negativeelectrode material in organic electrolyte except in very few cases wheresilicon and metal hydrides were used as the negative electrode materialsin aqueous alkaline electrolyte and carbonaceous materials and metalswere used as the negative intercalation materials in organicelectrolyte. The cause of the instability varies depending on theelectrolyte system and the negative electrode material. For zinc-air,sodium-air, magnesium-air, and lithium-air batteries, the instability ismainly because of the metal dissolution/deposition process during thecharge/discharge cycling process. In U.S. Patent Application, Pub. No.2006/0257744 A1, Burchardt disclosed the formulation of a zinc electrodefor electrochemically rechargeable zinc-air alkaline batteries. Thestability is still limited to tens of cycles because of the stabilitylimitation in zinc electrode. In U.S. Patent Application, Pub. No2007/0117007 A1, rechargeable lithium-air batteries were fabricated bydepositing a lithium-ion conductive solid coating on metallic lithium tolimit the corrosion of lithium by moisture and electrolyte. Thiscoating, however, is not expected to solve the stability issues becauseof the dramatic volume change of the lithium film during the lithiumdissolution/deposition process. In Patent Publication, Pub. No.WO/2010100636, Yair disclosed the use of a silicon negative electrode inan alkaline system as a primary air battery. The formed silicate ionsare almost impossible to be reduced back into silicon. Osada et al.disclosed the use of metal hydrides as the negative electrode materialsin the 218^(th) Electrochemical Society Meeting and a promising cyclingstability was reported. The cycling stability of metal hydrides,however, is limited to at most 1500 cycles as in nickel metal hydridealkaline batteries. In U.S. Patent Application, Pub. No. 2004/0241537A1, Okuyama et al. revealed the fabrication of an air battery withcarbonaceous materials and metals as the negative electrode material inan organic electrolyte. These negative materials stored energy through alithium ion intercalation process (faradic reactions) as being describedin the patent. For carbonaceous materials and metals to be used to asintercalation materials, the negative electrode has to becharged/discharged to very low voltage potentials (generally <0.3 V vs.Li/Li⁺), which may limit the long-term stability and cause safetyissues. Carbonaceous materials generally act as electro-inert materialsin aqueous solution, but they can become electro-active when they arecharged/discharged to very low potentials in organic electrolyte(generally <0.3 V vs. Li/Li⁺). An electro-active carbonaceous materialwill experience volume expansion/contraction as other negative electrodematerials, which limits its cycling stability from tens to a fewthousands of cycles. In comparison, an electro-inert carbonaceousmaterial may be cycled for millions of cycles. Moreover, electro-activecarbonaceous materials may be limited in energy capacities. Thetheoretical energy capacity for graphite is 374 mAh/g. In comparison,the theoretical energy capacity for silicon is 4200 mAh/g. On the otherhand, non-lithium metals can form alloys with lithium. These metals willexperience dramatic volume expansion/contraction during charge/dischargecycling. For example, the volume expansion for tin is 676% when it isfully charged in a lithium ion battery. A battery with a pure metalnegative electrode will have limited cycling stability because of thevolume expansion/contraction. In this sense, prior art negativematerials for non-aqueous air batteries are limited either in specificcapacity (carbons, 374 mAh/g or 834 mAh/cm³ for graphite) or in cyclingstability (lithium and metals). It would be necessary to develop anegative material that provides both high capacity and good cyclingstability for air batteries.

The instability of the metal electrode has limited metal-air batteriesto mainly primary (non-rechargeable) batteries unless the metal ismechanically refueled, which is similar to the operation concept with aliquid or gaseous fuel. Besides being limited in the negative electrodematerials, the prior art metal-air batteries have several otherlimitations. The prior art metal-air batteries are limited in using airelectrode as the positive electrode, while the possibility of using airelectrode as the negative electrode has not been disclosed. The priorart aqueous metal-air batteries are limited in using a highly corrosivealkaline solution as the electrolyte, while the possibility of using amild neutral solution or an acidic solution has not been disclosed.

SUMMARY OF THE INVENTION

A general object of this invention, therefore, is to provideelectrochemically rechargeable energy storage devices with goodstability based on various combinations of air electrodes, electro-inertmaterials, electro-active materials, and electrolytes.

Various embodiments relate to new rechargeable energy storage devicesbased on the operating concepts from electrochemical capacitors,batteries and fuel cells.

In at least one embodiment, a hybrid device comprises a capacitiveelectrode with the similar function as in an electrochemical capacitorand a second electrode with the same function as an air electrode fromrechargeable metal-air batteries. One electrode may include a capacitivematerial that stores energy through non-faradic reactions and the otherelectrode may include a material that acts as a catalyst or catalystsfor both oxygen reduction and evolution. This energy storage device isexpected to have improved energy density over symmetric double layercapacitors by greatly reducing or nearly eliminating the weight of theair electrode. For example, the energy density of an electrochemicalcapacitor can be calculated as1/(m_(T)C_(T))=1/(m_(n)C_(n))+1/(m_(p)C_(p)) as we discussed above. Withan efficient catalyst, the theoretical capacitance for the air electrodeis unlimited large. Therefore, the weight for the air electrode can benegligible small compared to the material weight at the negativeelectrode. The specific capacitance of the device will be the same asthe specific capacitance of the negative electrode. For an activatedcarbon with 280 F/g capacity, the total capacitance of a capacitor withair electrode is 280 F/g, while the value is 70 F/g for thecorresponding symmetric activated carbon/activated carbon capacitor.

In at least one embodiment, a hybrid device comprises a capacitiveelectrode with the similar function as in an electrochemicalcapacitor/battery and a second electrode with the same function as anair electrode from rechargeable metal-air batteries. The hybrid energystorage device will have improved cycling stability and/or improvedenergy density over the prior art metal-air batteries by using wiselychoosed negative electrode materials such as electro-inert carbonaceousmaterials, electro-active silicon/carbon composites, and electro-activecompounds. In one example, the cycling stability of zinc-air batterieswill be improved if zinc is replaced by a carbonaceous material sincethe carbonaceous material can reversibly store energy throughnon-faradic reactions. In another example, the metallic lithium negativeelectrode may be replaced with a silicon/carbon composite in non-aqueouslithium-air batteries. The cycling stability of the composite negativeelectrode could be much better than pure lithium as being proved inlithium-ion batteries research. Silicon tends to form alloys withlithium ions during the charge process and release lithium ions duringthe discharge process. Unlike lithium, silicon maintains its solidmorphology during the cycling process. By constraining the volume change(as high as 400%) with carbon, at least a few hundred charge/dischargecycles have been obtained for a silicon/carbon composite electrode in anon-aqueous electrolyte. Compared to prior art electro-activecarbonaceous material as the negative material, a silicon/carboncomposite could provide much higher energy density (theoretical specificcapacity for silicon: 4200 mAh/g) while maintaining a comparable cyclingstability. In a third example, a compound such as Li₄Ti₅O₁₂ could beused as the negative electrode material. The volumeexpansion/contraction during the lithium insertion/extraction process isnegligible for Li₄Ti₅O₁₂. A hybrid device built on Li₄Ti₅O₁₂ will haveimproved cycling stability over the prior art metal-air batteries.

In at least one embodiment, the air electrode could be used as thenegative electrode instead of using as a positive electrode as in theprior art air batteries. The application of air electrode as thenegative electrode may provide us a safe rechargeable energy storagedevice with good energy density. Current safe lithium-ion batteriesfocus on using Li₄Ti₅O₁₂ as the negative electrode material because ofits relatively high redox potential (˜1.5 V vs. Li/Li⁺) and negligiblevolume expansion/contraction during cycling. The theoretical energydensity of this negative material, however, is only 175 mAh/g, whichlimits the overall energy density of an energy storage device. Thedevice's energy density could be doubled with an air electrode operatedat similar redox potentials by assuming the positive electrode has acapacity of 175 mAh/g.

In at least one embodiment, the electrolyte could be neutral solution.The prior art aqueous metal-air batteries are limited in using highlyalkaline electrolytes. The high corrosive properties of highly alkalinesolutions may limit the cycling stability of an air catalyst. A mildneutral electrolyte may extend the stability of the air catalyst.Moreover, the operating voltage window of the device may be extendedsince the potentials of oxygen reduction/evolution are expected to bepositively shifted because of a decrease in pH while the operatingpotential of the negative electrode could be maintained at similar rangebecause of the overpotential formed at the negative electrode.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic representation of a two-electrode asymmetricrechargeable energy storage device.

FIG. 2 is a schematic representation of a three-electrode asymmetricrechargeable energy storage device.

FIG. 3 is a schematic representation of electrochemical processes for anasymmetric rechargeable energy storage device and the correspondingmovement of ions during charging and discharging in an alkaline aqueouselectrolyte.

FIG. 4 is a schematic representation of electrochemical processes for anasymmetric rechargeable energy storage device and the correspondingmovement of ions during charging and discharging in an acidic aqueouselectrolyte.

FIG. 5 is a schematic representation of electrochemical processes for anasymmetric rechargeable energy storage device and the correspondingmovement of ions during charging and discharging in a neutral aqueouselectrolyte.

FIG. 6 is a schematic representation of electrochemical processes for anasymmetric rechargeable energy storage device and the correspondingmovement of ions during charging and discharging in an organicelectrolyte.

FIG. 7 is a schematic representation of electrochemical processes for anasymmetric rechargeable energy storage device with the air electrode asthe negative electrode and the corresponding movement of ions duringcharging and discharging in an organic electrolyte.

FIG. 8 is a plot illustrating time evolution of cell and air electrodepotentials during constant current charge/discharge cycling.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In various embodiments an asymmetric rechargeable energy storage deviceutilizes a capacitive material or materials as one electrode for chargestorage and an air electrode or electrodes as the other electrode orelectrodes for oxygen reduction and evolution. By definition, the airelectrode comprises catalyst/catalysts for both oxygen reductionreaction (ORR) and oxygen evolution reaction (OER). The air electrodemay be two catalytic reactive electrodes that can catalyze the ORR andOER separately. Based on the operational concept, the inventedasymmetric rechargeable energy storage device may have a variety ofdesigns and a variety of combinations of electrodes and electrolytes.

An example of a general structure of two-electrode device is illustratedin FIG. 1. The asymmetric rechargeable device may comprise a positiveelectrode consisting of a current collector and a catalyst or catalyststhat can effectively reduce oxygen during the discharge process andfacilitate oxygen evolution during the charge process, a negativeelectrode consisting of a porous material or materials that can storecharge at the electrode/electrolyte interface, a porous electricinsulating separator that allows ion but not electron transport, anelectrolyte that includes aqueous and non-aqueous solutions, gels,polymers, semi-solids, and solids.

The energy storage device may be designed as a three-electrode device(FIG. 2) to improve the device's stability. The three-electrode devicemay comprise two separate catalytic electrodes for the oxygen reductionreaction (ORR) and the oxygen evolution reaction (OER). The capacitiveelectrode may be located between the oxygen reduction catalyticelectrode and the oxygen evolution catalytic electrode. The ORRelectrode is electrically isolated during the charging process, so thatthis electrode is not affected by the high oxygen evolution potentialapplied to the OER electrode, which may extend the lifetime of the ORRelectrode.

In an asymmetric rechargeable device, current collectors may be madefrom conductive carbonaceous materials, non-reactive metals, or otherelectric conductive substances that are stable in contact with theelectrolyte in the range of working voltages. Unlike capacitors,structures of the two electrodes in the device are different from eachother. One electrode contains a capacitive material, which is similar toa capacitor or a battery. Basically, a film made of a capacitance-activematerial is coated or deposited on top of the current collector. Thefilm may comprise a capacitive material for energy storage, a conductiveadditive to improve the film's electric conductivity, and a polymerbinder to help maintain the integral structure of the film. An exampleof a capacitive material for the rechargeable device may comprise bothan electro-inert material and an electro-active material. Theelectro-inert material will provide long cycling stability, while theelectro-active material will provide high energy storage capacity. Theratio between two components may vary depending on the performancerequirement for the device. Generally, a higher ratio of electro-inertmaterial/electro-active material will be used for devices with longercycling stability, while a higher ratio of electro-activematerial/electro-inert material will be used for devices with higherenergy density. Depending on the device performance requirement, theratio of electro-inert material/electro-active material can be at leastabout 5%, at least about 20%, at least about 50%, and at least about90%. A second example of a capacitive material for the rechargeabledevice may comprise only an electro-inert material to provide longcycling stability for certain applications. A third example of acapacitive material for the rechargeable device may comprise only anelectro-active material that is superior to the prior art materials ineither cycling stability or specific energy capacity. In one example, asilicon/carbon composite may be used as the capacitive material in anorganic electrolyte to provide good cycling stability and large energycapacity. In another example, Li₄Ti₅O₁₂ may be used as the capacitivematerial to provide long cycling stability. In a third example, LiCoO₂may be used as the positive electrode in a non-aqueous electrolytesystem. Different from the capacitive electrode, the air electrodegenerally contains a porous air diffusion layer for the catalyst to beair accessible. A hydrophobic porous layer could be made to preventwater/moisture from entering the device and polar solvent includingwater from leaving the device. The device's performance will deterioraterapidly if the hydrophobic porous layer does not function well. Thecatalyst layer may deposit on top of the hydrophobic air diffusionlayer. Catalysts may include metals, metal oxides, functionalized carbonmaterials (nitrogen-doped carbon fibers for example), and metalsulfides. Since high surface area is preferred to achieve highreactivity, a catalyst is generally deposited onto carbonaceousmaterials with high surface areas. A bifunctional catalyst may be amixture of catalytic reactive materials for oxygen evolution andreduction reactions.

The asymmetric device concept can be applied to a variety of specificsystems based on the difference in electrolyte property. Five examplesare shown in FIGS. 3, 4, 5, 6, and 7. In all systems, the capacitiveelectrode may comprise a capacitive material, a binder, and a conductiveadditive. The binder can be organic or inorganic. The conductiveadditive can be any substance with good electric conductivity.Specifically, the conductive additive may be selected from carbon black,acetylene black, ketjen black, activated carbon, carbon nanowires,carbon nanotubes, graphite, graphene, and metal particles includingcopper, silver, nickel, titanium, aluminum, and conducting polymers. Thecapacitive material may be selected from an electro-inert material, anelectro-active material, and their mixtures. The electro-inert materialmay be selected from amorphous, semi-crystalline, or crystallinecarbonaceous materials. The semi-crystalline carbonaceous material maycomprise crystallinity in the range of 1% to 99%, <1%, and >99%. Thecarbonaceous material may include activated carbons, carbon fibers,multi-wall carbon nanotubes, double-wall carbon nanotubes, single-wallcarbon nanotubes, graphene, carbon nanocrystals, carbon nanoparticles,microporous carbons (pore size <2 nm), mesoporous carbons (pore size 2nm-50 nm), macroporous carbons (pore size >50 nm), carbon nanocages,carbon nano-onions, carbon black, and fluorinated carbons. Theelectro-active material may be selected from any material that does notdissolve as ions during the cycling. The selection of a capacitivematerial will rely on its reactivity and stability in a specificelectrolyte system. Composites of electro-inert materials andelectro-active materials may be used to improve the cycling stability ofthe electro-active materials. The air catalyst may comprise any oxygenreduction catalyst and oxygen evolution catalyst that has been studiedfor fuel cells and metal-air batteries. A bifunctional catalyst that cancatalyze both oxygen reduction and oxygen evolution may also be used. Anoxygen reduction catalyst may serve as a bifunctional catalyst with MnO₂as one example. These oxygen reduction and bifunctional catalysts mayinclude but not limited to metals (Au, Ag, Pt, and their alloys),pyrolyzed metal porphyins (for example: iron tetra-methoxylphenylporphyrin, cobalt tetraphenyl porphyrin), metal oxides (spinelMn_(x)Co_(3-x)O₄, Bi₂Ir₂O_(7-z), Pb₂Ru₂O_(6.5), MnO₂, LaMnO₃,CaMn₄O_(x), La_(0.1)Ca_(0.9)MnO₃, LaCoO₃, LaNiO₃, LaCoSrO₃,La_(0.6)Ca_(0.4)CoO₃, Nd(or La)_(0.5)Sr_(0.5)CoO₃,La_(1-x)A_(x)Fe_(1-y)Mn_(y)O₃ (A=Sr, Ca),La_(0.6)Ca_(0.4)Co_(0.8)B_(0.2)O₃ (B═Mn, Fe, Co, Ni, or Cu),La_(0.6)Ca_(0.4)CoO_(3-x), La_(0.7)Ca_(0.3)CoO_(3-x), pyrochlore-basedcatalysts (A₂B₂O₆O′, A: Pb; B: Ru, Ir), metal hydroxides (NiOOH,Co(OH)₂, FeOOH), metal nitrides (Mn₄N), and functionalized carbons(nitrogen-doped carbonaceous materials). The oxygen evolution reactioncatalyst may be selected from metals (Ni, Co, Ag, inter-metallic alloys(often containing significant amounts of Ni, Co or Fe)), metal oxides(spinels (particularly nickelites, cobaltites, and ferrites),perovskites, IrO₂, RuO₂, FeWO₄, LaNiO₃), metal sulfides (NiS), metalcarbides (WC), and metal phosphates (cobalt phosphate). The selection ofan air catalyst will depend on its reactivity and stability in aspecific electrolyte.

For the rechargeable device, the electrolyte can be liquid, semi-solid,and solid. Electrolytes developed for batteries and supercapacitors canbe used in this device. The basic requirement for a good electrolyte isthat it can provide ions for energy storage. Based on this requirement,a variety of electrolytes could be used. Suitable electrolytes includebut are not limited to aqueous alkaline solutions, aqueous acidicsolutions, aqueous neutral solutions, organic solutions, ionic liquids,gels, polymers, and inorganic solids. The choice of an electrolyte willrely on the requirement for the performance of the device since theworking mechanism of the device will be determined by the electrolyte.

For the rechargeable device, the current collector can be selected fromNi, Ti, Fe, Al, Cu, conductive carbons, conductive oxides, andconductive polymers.

For all systems, oxygen will be introduced as a reactant. Oxygen can beintroduced by a variety of methods. Oxygen can be fed into the systemfrom air or a pure oxygen source. Oxygen may be provided from theelectrolyte solution as molecular oxygen. Either a closed-loop or opensystem may be used for oxygen circulation.

FIG. 3 shows an asymmetric rechargeable energy storage device withalkaline solution as the electrolyte. The alkaline solution can be madeby dissolving an alkaline metal hydroxide including LiOH, NaOH, and KOHin water. During charging, the air electrode catalyzes the oxygenevolution reaction by decomposing hydroxide ions to produce oxygen gas.Meanwhile, alkaline metal cations such as potassium, sodium, and lithiumions will move to the negative electrode through the electrostaticattractions. During discharging, oxygen is reduced at the air electrodewhile the absorbed cations are released back into the electrolyte.

In an alkaline asymmetric energy storage device, the oxygen reductionreaction catalyst may be selected from Ag, pyrolyzed FeTMPP (irontetra-methoxylphenyl porphyrine), Mn₄N, spinel Mn_(x)Co_(3-x)O₄,Pb₂Ru₂O_(6.5), MnO₂, LaMnO₃, La_(0.1)Ca_(0.9)MnO₃, LaCoO₃, LaNiO₃,LaCoSrO₃, La_(0.6)Ca_(0.4)CoO₃, Nd(or La)_(0.5)Sr_(0.5)CoO₃,pyrochlore-based catalysts (A₂B₂O₆O′, A: Pb; B: Ru, Ir), NiOOH, Co(OH)₂,and FeOOH. The oxygen evolution reaction catalyst may be selected fromNi, Co, Ag, inter-metallic alloys (often containing significant amountsof Ni, Co or Fe), mixed oxides including spinels (particularlynickelites, cobaltites, and ferrites), perovskites, IrO₂, RuO₂, FeWO₄,NiS, WC, LaNiO₃, and cobalt phosphate. Bifunctional catalysts maycomprise both oxygen reduction catalysts and oxygen evolution catalystsin certain ratios.

Different from the current metal-air batteries with using pure metals asthe negative electrode materials, suitable negative electrode materialsin this system may contain carbonaceous materials, uranates, lithiumtitanium phosphate, organic-inorganic compounds, polyoxometalates, andconducting polymers including polyaniline.

FIG. 4 shows the operation mechanism of an asymmetric rechargeableenergy device with an acidic electrolyte. The electrolyte can beselected from H₂SO₄ and H₃PO₄. During charging, the air electrodecatalyzes the oxygen evolution reaction by decomposing water to produceoxygen gas. Meanwhile, positive charged proton ions will move to thenegative electrode to be adsorbed/stored at the capacitive electrode.During discharging, the air electrode reduces oxygen back into water andthe adsorbed/stored proton ions are released back into the solution.

For the acidic asymmetric energy storage device, the capacitive materialmay be selected from carbonaceous materials and electro-active materialsthat are stable in acid solutions. These materials may compriseconductive polymers (polyanilion and polypyrrole), Pb, TiO₂, Mo_(x)N(x=1 and 2), MoO₃, WO₃, RuO₂, polyoxometalates, and silicon.

Suitable oxygen reduction catalysts may include pyrolyzed transitionmetal phthalocyanin (iron, cobalt), Pt, Pd, CoPd, CoPt. Oxygen evolutioncatalysts may include SnO₂, RuO₂, and IrO.

FIG. 5 shows the expected operation mechanism of an asymmetricrechargeable energy device with a neutral electrolyte. The electrolytecan be made by dissolving a salt or salts in water. Suitable saltsinclude, but are not limited to, A_(x)B_(y) (A: ammonium, lithium,sodium, potassium, magnesium, calcium, aluminum; B: NO₃ ⁻, Cl⁻, SO₄ ²⁻,PO₄ ³⁻, BO₃ ⁻). The electrolyte solution may be weakly basic or acidic.During charging, the positive charged metal and proton ions move to thenegative electrode, while water is decomposed to release oxygen at theair electrode. During discharging, O₂ is reduced at the air electrode,while adsorbed metal cations are released back into the electrolyte.

Suitable aqueous neutral electrolytes include aqueous solutions ofcarbonates of alkaline metals, chlorides of alkaline metals, sulfates ofalkaline metals, borates of alkaline metals, phosphates of alkalinemetals, ammonium salts, or their mixtures.

Suitable negative electrode materials for neutral solution may compriseamorphous, semi-crystalline, and crystalline carbonaceous materials,conducting polymers, polyoxometalates, lithium intercalated materialssuch as lithium titanium phosphate and lithium vanadium oxides, tinoxide, molybdenum oxide, indium oxide, and bismuth oxide.

Suitable oxygen reduction catalysts may comprise pyrolyzed transitionmetal phthalocyanines, transition metal tetramethoxyphenylporphyrin(TMPP), and MnO₂. Suitable oxygen evolution catalysts may include butnot limited to metal oxide (mainly MnO₂), transition metal mixed oxideswith spinellic structure (AB₂O₄, where A=a bivalent and B=a trivalentmetal ion), transition metal mixed oxides with perovskite (ABO₃, whereA=mainly La and B═Co or Ni) structure.

FIG. 6 shows the expected operation mechanism of an asymmetricrechargeable energy device with an organic electrolyte. Ametal-containing salt such as LiPF₆ is used only for illustrationpurposes. During charging, the positive charged lithium ions move to thenegative electrode, while lithium oxide is decomposed to release oxygenand lithium ions at the air electrode. During discharging, O₂ is reducedat the air electrode to form lithium oxide, while adsorbed lithiumcations are released back into the electrolyte.

Organic solvents, ionic liquids, polymer gels, polymers, solid ionicconductors, and salts used for lithium-ion batteries and supercapacitorscan be used for this device. Suitable salts may include alkaline metals,alkaline earth metals, and any other metal or organic group that canform ions in the electrolyte. Typical salts containing lithium includeLiClO₄, LiPF₆, LiBF₄, LiAsF₆, LiC(SO₂CF₃)₃, LiN(SO₂CF₃)₂, LiSO₃CF₃,LiBr, lithium bis(oxatlato)borate (LiBOB), and LiI. Polymer electrolytesmay include poly(ethylene oxide) (PEO), poly(propylene oxide) (PPO),poly(acrylonitrile) (PAN), poly(methyl methacrylate) (PMMA), poly(vinylchloride) (PVC), poly(vinyliden fluoride) (PVdF). Solid inorganic ionicconductors include but not limited to LiX (X: F, Cl, Br, I), LiAlCl₄,Li₃N, Li₃PO₄, Li₄WiO₄, LiTi₂(PO₄)₃, Li₃(PO_(4-x))N_(x) (LiPON),inorganic materials occupying perovskite-, NASICON- and Li₄SiO₄-typecrystal structures.

Suitable negative electrode material may comprise partially or fullyelectro-inert amorphous carbons, semi-crystalline carbons, crystallinecarbons that are charged/discharged to above a certain potential level(1.0 V vs. Li/Li⁺, 0.5 V vs. Li/Li⁺ or 0.3 V vs. Li/Li⁺ for example). Inanother case, the negative electrode material may be a compositecontaining an electro-active carbonaceous material and a non-carbonelement (silicon, tin, germanium, arsenic, antimony, tellurium, orboron). The electro-active carbonaceous material is to help release theexpansion/contraction stress of the non-carbon material during thecharge/discharge process, while the electro-active non-carbon materialprovides the high energy storage capacity through faradic reactions. Forthe carbonaceous material to work efficiently, the composite ispreferred to be made in a way that most of the non-carbon electro-activeparticles are in contact with carbon particles. As one example, each ofthe non-carbon particles can be covered with a continuous carbon coatingsimilar to a core-shell structure. As another example, at least onenon-carbon particles may be dispersed in a carbon matrix. As a thirdexample, non-carbon particles may be coated on the surface ofcarbonaceous materials including but not limited to carbon nanofibers,carbon nanotubes, and graphene. The composite in this invention is notpreferred to be made by simply mixing at least two componentsmechanically unless aggregates of non-carbon particles can be brokeninto smaller aggregates in nano sizes (<100 nm preferred). As a forthexample, the non-carbon active material may be covered a mechanicallyflexible conductive polymer. The conductive polymer constrains thevolume expansion/contraction of the non-carbon particles to increasetheir cycling stability.

Suitable negative electrode material may comprise a composite made froma carbonaceous material and an element. The element may be a metalselected from alkaline earth metals, transition metals, Al, Ga, In, Sn,Pb, and Bi. To ensure the cycling stability of the negative compositematerial, the element can not be dissolved during the charge process.For example, in lithium-ion electrolyte, metallic lithium can not beused. In another example, metallic Mg can not be used when Mg²⁺ is theactive ion in the electrolyte for energy storage. The element may be asemimetals selected from B, Si, Ge, As, and Sb. To ensure the cyclingstability, a carbonaceous material such as carbon nanotubes and graphenehas to be incorporated to release the volume expansion/contraction ofthe elemental material during the cycling process.

Suitable negative electrode material may comprise a compound includingbut not limited to lithium titanium oxide, transition metal oxides (ironoxide, molybdenum oxide, manganese oxide, cobalt oxide, molybdenumoxide, manganese oxide, vanadium oxide, nickel oxide, RuO₂, titaniumoxide), tin oxide, antimony oxide, lead oxide, bismuth oxide, metalsulfides (TiS₂, MoS₂, FeS₂, FeS, TaS₂), metal selenides (MnSe, ZnSe,SnSe, Sb₂Se₃, and Mo₆Se₆), metal nitrides (Li₇MnN₄, Li₃FeN₂,Li_(2.6)Co_(0.4)N, Li_(2.7)Fe_(0.3)N), metal phosphides (MnP₄, FeP₂,Li₇MP₄ (M=Ti, V, Mn), CoP₃), metal borates (FeBO₃, VBO₃, for example),metal sulfates, polyoxometalates, conducting polymers, and theirmixtures.

Air electrode materials developed for rechargeable lithium-air batteriescan be used in this system. Suitable oxygen reduction catalysts maycomprise carbonaceous materials, MnO_(x), and transition metalphthalocyanine (transition metal: Fe, Co). Suitable oxygen evolutioncatalysts may include nickel foam. Other catalysts that have beendeveloped for aqueous systems (fuel cells, metal-air batteries) may beuseful for the organic hybrid energy storage device as well.

Without being bound by any particular theory, FIG. 7 shows the expectedoperation mechanism for a rechargeable energy storage device with theair electrode acting as a negative electrode. NaPF₆ is used as the saltfor illustration purposes. The reason to choose NaPF₆ is that thetheoretical redox potential for the air electrode with Na⁺ salt is 1.94V vs. Li/Li⁺, which is suitable for a negative electrode. Duringcharging, the positive charged sodium ions move to the negativeelectrode, where they combine with the reduced O₂ to form sodium oxide.The negative charged PF₆ ⁻ ions are attracted to the positive electrodeto be adsorbed at the surface of carbon materials. During discharging,sodium oxide is oxidized at the air electrode to release sodium ions andoxygen, while adsorbed PF₆ ⁻ anions are released back into theelectrolyte.

Organic solvents, ionic liquids, polymer gels, polymers, solid ionicconductors, and salts used for lithium-ion batteries and supercapacitorscan be used for this device. Suitable salts may include alkaline metals,alkaline earth metals, and any other metal (for example Zn and Al) ororganic group that can form ions in the electrolyte. Polymerelectrolytes may include poly(ethylene oxide) (PEO), poly(propyleneoxide) (PPO), poly(acrylonitrile) (PAN), poly(methyl methacrylate)(PMMA), poly(vinyl chloride) (PVC), poly(vinyliden fluoride) (PVdF).Solid inorganic ionic conductors include but not limited to LiX (X: F,Cl, Br, I), LiAlCl₄, Li₃N, Li₃PO4, Li₄WiO₄, LiTi₂(PO₄)₃,Li₃(PO_(4-x))N_(x) (LiPON).

Developed cathode materials for lithium ion batteries are suitablecapacitive materials for the device. These materials may comprise butnot limited to inorganic materials with layered, spinel, perovskitestructures, carbons, and organic materials. Any material that canprovide high redox potentials (preferably >2 V vs. Li/Li⁺) can be usedas the positive electrode material. Capacitive material may comprise butnot limited to carbonaceous materials, fluorinated carbonaceousmaterials, metal oxides (LiCoO₂, LiNiO₂, LiMn₂O₄, V₂O₅, V₆O₁₃, LiV₃O₈,and their mixtures), metal phosphates (LiTi₂(PO₄)₃, LiFePO₄, LiMnPO₄,LiNiPO₄, LiCoPO₄, VOPO₄, Li₄P₂O₇, LiVPO₄, Li₃V₂(PO₄)₃), metal fluorides(LiVPO₄F, fluorine-doped oxides), metal sulfates (Fe₂(SO₄)₃, Mn₂(SO₄)₃),metal borates (LiFeBO₃, LiMnBO₃, LiNiBO₃, LiCoBO₃), metal vanadates(metal: Co, Fe, Zn, Ni, Cu, Mg), bromine, iodine, sulfur, selenium, andtheir mixtures.

Air electrode materials developed for fuel cells, rechargeablelithium-air batteries, and rechargeable zinc-air batteries can be usedin this system.

EXAMPLES

A two-electrode test cell of the asymmetric energy storage device wasfabricated by using an air electrode from a commercial zinc-air batteryas the positive electrode and an activated carbon capacitive electrodeas the negative electrode. A mercury-mercuric oxide (Hg/HgO) referenceelectrode was added into the cell to monitor the potential evolution ofthe air electrode during charge and discharge cycles. The air electrodewas obtained by dissembling a commercial zinc-air button cell and thenrinsing the electrode with de-ionized water. 1 M KOH was used as theelectrolyte for the test cell. Electrochemical testing was carried outin a battery testing instrument (ARBIN). A graph of constant currentcharge/discharge curves is shown in FIG. 8. The charge/discharge curvesare almost linear, which is typical for double-layer capacitance(non-faradic reactions). The cell is stable for the tested cycles. Novisually observable decrease in charging/discharge time is observed. Theair electrode potential during the charge/discharge cycles keepsconstant, confirming that the air electrode acts as a catalyst insteadof a capacitive electrode. Otherwise, the potential at the air electrodewould increase during charging and decrease during discharging. Theexperiment shows that a stable asymmetric rechargeable energy storagedevice can be made from an air electrode and a stable capacitivematerial.

Thus, the inventors have disclosed an invention wherein at least oneembodiment includes a rechargeable energy storage device comprising anair electrode where oxygen reduction and evolution takes place, acapacitive electrode where a non-faradic reaction contributes to atleast about 5% of the total specific capacity, an ion-permeableseparator, and an electrolyte. For the capacitive electrode, thenon-faradic reaction may contribute to at least about 20% of the totalspecific capacity. It is also possible that the non-faradic reaction maycontribute to at least about 50% or 90% of the total specific capacity.

The air electrode may be used as the positive electrode while thecapacitive electrode is the negative electrode similar to the prior artmetal-air batteries. The air electrode may also be used as the negativeelectrode while the capacitive electrode is used as the positiveelectrode.

The air electrode may have a porous hydrophobic layer to let air in andout, while restricts the egression of solvent from the device and theingression of moisture from air.

The air electrode may be fabricated in a way that two electrodes will beused to carry out oxygen reduction and evolution separately.

The air electrode may have at least one catalyst that can catalyzeoxygen reduction and evolution.

The oxygen reduction catalyst may be selected from metals, metal oxides,pyrolyzed metal porphyrins, metal nitrides, metal hydroxides, andfunctionalized carbons.

The metals may comprise Ag, Pt, Au, and their alloys.

The metal oxides may comprise spinel Mn_(x)Co_(3-x)O₄, Bi₂Ir₂O_(7-z),Pb₂Ru₂O_(6.5), MnO₂, LaMnO₃, CaMn₄O_(x), La_(0.1)Ca_(0.9)MnO₃, LaCoO₃,LaNiO₃, LaCoSrO₃, La_(0.6)Ca_(0.4)CoO₃, Nd(or La)_(0.5)Sr_(0.5)CoO₃,La_(1-x)A_(x)Fe_(1-y)Mn_(y)O₃ (A=Sr, Ca),La_(0.6)Ca_(0.4)Co_(0.8)B_(0.2)O₃ (B═Mn, Fe, Co, Ni, or Cu),La_(0.6)Ca_(0.4)CoO_(3-x), La_(0.7)Ca_(0.3)CoO_(3-x), pyrochlore-basedcatalysts (A₂B₂O₆O′, A: Pb; B: Ru, Ir).

The pyrolyzed metal porphyins may comprise iron tetra-methoxylphenylporphyrin and cobalt tetraphenyl porphyrin.

The metal nitrides may comprise Mn₄N.

The metal hydroxides may comprise NiOOH, Co(OH)₂, and FeOOH.

The functionalized carbons may comprise nitrogen-doped carbonaceousmaterials.

The oxygen evolution catalyst may be selected from metals, metal oxides,metal sulfides, metal carbides, and metal phosphates.

The metals may comprise Ni, Co, Ag, and inter-metallic alloys (oftencontaining significant amounts of Ni, Co or Fe).

The metal oxides may comprise spinels (particularly nickelites,cobaltites, and ferrites), perovskites, IrO₂, RuO₂, FeWO₄, LaNiO₃.

The metal sulfides may comprise NiS.

The metal carbides may comprise WC.

The metal phosphates may comprise cobalt phosphate.

The bi-functional oxygen reduction and evolution catalyst may beselected from the group comprising metals, pyrolyzed metal porphyins,metal oxides, metal hydroxides, metal nitrides, and functionalizedcarbons.

The metals may comprise Ag, Pt, Au, and their alloys.

The pyrolyzed metal porphyins may comprise iron tetra-methoxylphenylporphyrin, cobalt tetraphenyl porphyrin.

The metal oxides may comprise spinel Mn_(x)Co_(3-x)O₄, Bi₂Ir₂O_(7-z),Pb₂Ru₂O_(6.5), MnO₂, LaMnO₃, CaMn₄O_(x), La_(0.1)Ca_(0.9)MnO₃, LaCoO₃,LaNiO₃, LaCoSrO₃, La_(0.6)Ca_(0.4)CoO₃, Nd(or La)_(0.5)Sr_(0.5)CoO₃,La_(1-x)A_(x)Fe_(1-y)Mn_(y)O₃ (A=Sr, Ca),La_(0.6)Ca_(0.4)Co_(0.8)B_(0.2)O₃ (B═Mn, Fe, Co, Ni, or Cu),La_(0.6)Ca_(0.4)CoO_(3-x), La_(0.7)Ca_(0.3)CoO_(3-x), pyrochlore-basedcatalysts (A₂B₂O₆O′, A: Pb; B: Ru, Ir).

The metal hydroxides may comprise NiOOH, Co(OH)₂, and FeOOH.

The metal nitrides may comprise Mn₄N.

The functionalized carbons may comprise nitrogen-doped carbonaceousmaterials.

The current collector may be selected from metals, conductive carbons,conductive oxides, and conductive polymers.

The metals may comprise Ni, Ti, Fe, Al, and Cu.

The capacitive electrode may comprise at least one material selectedfrom electro-inert materials.

The electro-inert material may be selected from activated carbons,porous carbons, carbon foams, carbon fibers, carbon nanotubes, graphene,and carbon nanoparticles, which provide a non-faradic reaction.

The capacitive electrode may comprise an electro-active material.

The electro-active material may be selected from metals that can formalloys with the active metal cations from the electrolyte, semimetals,nonmetals, metal oxides, metal borates, metal sulfides, metal selenides,metal phosphides, metal nitrides, fluorinated carbons, metal phosphates,metal fluorides, metal sulfates, metal borates, metal vanadates,polyoxometalates, conductive polymers, and their mixtures, which providea faradic reaction.

The capacitive material may be a mixture or composite of at least oneelectro-inert material and at least one electro-active material.

The electrolyte may be an aqueous solution containing acid, base, salt,and their mixtures.

The base may comprise LiOH, NaOH, and KOH;

The acid may comprise H₂SO₄ and H₃PO₄.

The salt may comprise A_(x)B_(y) (A: ammonium, lithium, sodium,potassium, magnesium, calcium, aluminum; B: NO₃ ⁻, Cl⁻, SO₄ ²⁻, PO₄ ³⁻,BO₃ ⁻).

The electrolyte may be a non-aqueous solution.

The non-aqueous solution may be an organic solvent, a polymer, a polymergel, an ionic liquid, an ion-conductive solid.

The organic solvent may contain ethylene carbonate, diethyl carbonate,propylene carbonate, and acetonitrile.

The ion-conductive solid may be selected from lithium titanium phosphateand materials occupying perovskite-, NASICON- and Li₄SiO₄-type crystalstructures.

In one embodiment, the rechargeable energy storage device has onenegative air electrode, a positive capacitive electrode, anion-permeable separator, and a non-aqueous electrolyte.

The positive capacitive electrode contains at least one material forcharge storage.

The capacitive material may be selected from carbonaceous materials,fluorinated carbons, sulfur, selenium, iodine, bromine, carbonaceousmaterials, metal fluorides, metal oxides, metal sulfates, metalphosphates, metal borates, metal vanadates, and their mixtures.

Metal fluorides may contain fluorine-doped metal oxides and LiVPO₄F.

Metal oxides may comprise LiCoO₂, LiNiO₂, LiMn₂O₄, and their mixtures.

Metal sulfates may comprise Fe₂(SO₄)₃ and Mn₂(SO₄)₃.

Metal phosphates may comprise LiTi₂(PO₄)₃, LiFePO₄, LiMnPO₄, LiNiPO₄,LiCoPO₄, VOPO₄, Li₄P₂O₇, LiVPO₄, and Li₃V₂(PO₄)₃.

Metal borates may comprise LiFeBO₃, LiMnBO₃, LiNiBO₃, LiCoBO₃, and theirmixtures.

Metal vanadates may comprise Co₂V₂O₇, Ni₂V₂O₇, Fe₂V₂O₇, Mn₂V₂O₇,Zn₂V₂O₇, Cu₂V₂O₇, and Mg₂V₂O₇.

In one embodiment, the rechargeable energy storage device has onepositive air electrode, one negative capacitive electrode, anion-permeable separator, and a non-aqueous electrolyte.

The capacitive electrode contains at least one composite material orcompound.

The composite material may be selected from a carbonaceous material anda second material comprising semimetals and metals. These metals willnot dissolve during the discharge process. For example, non-lithiummetals will be used when the non-aqueous electrolyte contains a lithiumsalt. For electrolyte containing a lithium salt, the metals may beselected from alkaline earth metals, transition metals, Al, Ga, In, Sn,Pb, and Bi.

The semi-metals may be selected from B, Si, Ge, As, and Sb.

The compound may be selected from metal oxides, metal sulfides, metalselenides, metal phosphides, metal borates, and metal nitrides.

Metal oxides may comprise lithium titanium oxide, transition metaloxides (iron oxide, molybdenum oxide, manganese oxide, cobalt oxide,molybdenum oxide, manganese oxide, vanadium oxide, nickel oxide, RuO₂,titanium oxide), tin oxide, antimony oxide, lead oxide, and bismuthoxide.

Metal sulfides may comprise TiS₂, MoS₂, FeS₂, FeS, and TaS₂.

Metal selenides may comprise MnSe, ZnSe, SnSe, Sb₂Se₃, and Mo₆Se₆.

Metal phosphides may comprise MnP₄, FeP₂, Li₇MP₄ (M=Ti, V, Mn), CoP₃.

Metal borates may comprise FeBO₃ and VBO₃.

Metal nitrides may comprise Li₇MnN₄, Li₃FeN₂, Li_(2.6)Co_(0.4)N, andLi_(2.7)Fe_(0.3)N.

Thus, while only certain embodiments have been specifically describedherein, it will be apparent that numerous modifications may be madethereto without departing from the spirit and scope of the invention. Itis a goal of the invention to achieve one or more objects of theinvention, although the invention may be practiced without the fullachievement of any one of these objects. Further, acronyms are usedmerely to enhance the readability of the specification and claims. Itshould be noted that these acronyms are not intended to lessen thegenerality of the terms used and they should not be construed torestrict the scope of the claims to the embodiments described therein.

What is claimed is:
 1. A hybrid rechargeable energy storage devicecomprising: an air electrode, wherein an electrochemical processcomprising reduction and evolution of oxygen takes place; a capacitiveelectrode comprising a double layer electrochemical capacitor thatstores energy through non-faradic reaction; a separator which ision-permeable; and an electrolyte containing ions for non-faradic andfaradic reactions, wherein said capacitive electrode comprises at leastone material selected from electro-inert materials, said at least onematerial is configured to provide a non-faradic reaction, wherein acapacitive electrode process comprises a non-faradic reaction whichcontributes to the overall specific capacitance of the capacitiveelectrode.
 2. The hybrid rechargeable energy storage device of claim 1,wherein the capacitive electrode process comprises a non-faradicreaction which contributes to at least about 20% of the overall specificcapacitance of said capacitive electrode.
 3. The hybrid rechargeableenergy storage device of claim 1, wherein the capacitive electrodeprocess comprises a non-faradic reaction which contributes to at leastabout 50% of the overall specific capacitance of said capacitiveelectrode.
 4. The hybrid rechargeable energy storage device of claim 1,wherein the capacitive electrode process comprises a non-faradicreaction which contributes to at least about 90% of the overall specificcapacitance of said capacitive electrode.
 5. The hybrid rechargeableenergy storage device of claim 1, wherein said air electrode is thepositive electrode and said capacitive electrode is the negativeelectrode of said rechargeable energy storage device.
 6. The hybridrechargeable energy storage device of claim 1, wherein said airelectrode is the negative electrode and said capacitive electrode is thepositive electrode of said rechargeable energy storage device.
 7. Thehybrid rechargeable energy storage device of claim 1, wherein said airelectrode comprises a porous gas-diffusion layer, wherein ingress andegress of oxygen is achieved through the porous gas-diffusion layer. 8.The hybrid rechargeable energy storage device of claim 1, wherein saidair electrode comprises two separated electrodes, and wherein thereduction and evolution of oxygen take place at individual separatedelectrodes.
 9. The hybrid rechargeable energy storage device of claim 1,wherein said air electrode contains one or more catalysts enablingreduction and evolution of oxygen.
 10. The hybrid rechargeable energystorage device of claim 1, wherein said air electrode comprises at leastone catalyst selected from metals, pyrolyzed metal porphyrins, metaloxides, metal hydroxides, metal nitrides, and functionalizedcarbonaceous materials, for oxygen reduction.
 11. The hybridrechargeable energy storage device of claim 1, wherein said airelectrode comprises at least one catalyst selected from metals, metaloxides, metal sulfides, metal carbides, and metal phosphates, for oxygenevolution.
 12. The hybrid rechargeable energy storage device of claim 1,wherein said air electrode comprises at least one bi-functional catalystselected from the group comprising metals, pyrolyzed metal porphyins,metal oxides, metal hydroxides, metal nitrides, and functionalizedcarbonaceous materials.
 13. The hybrid rechargeable energy storagedevice of claim 1, wherein said air electrode comprises an electricallyconductive current collector selected from metals, conductive carbons,conductive oxides, and conductive polymers.
 14. The rechargeable energystorage device of claim 1, wherein said at least one material isselected from electro-inert materials comprising: activated carbons,porous carbons, carbon foams, carbon fibers, carbon nanotubes, graphene,and carbon nanoparticles, which provide a non-faradic reaction.
 15. Thehybrid rechargeable energy storage device of claim 1, wherein saidcapacitive electrode comprises at least one material selected fromelectro-active materials, comprising metals that can form alloys withthe metal cations from electrolyte during charging, semimetals,nonmetals, metal oxides, metal borates, metal sulfides, metal selenides,metal phosphides, metal nitrides, fluorinated carbons, metal phosphates,metal fluorides, metal sulfates, metal borates, metal vanadates,polyoxometalates, conductive polymers, and their mixtures, which providea faradic reaction.
 16. The hybrid rechargeable energy storage device ofclaim 1, wherein said capacitive electrode comprises a mixture orcomposite of at least one electro-inert electrode material providing anon-faradic reaction and at least one electro-active electrode materialproviding a faradic reaction.
 17. The hybrid rechargeable energy storagedevice of claim 1, wherein said electrolyte comprises an aqueoussolution containing a base.
 18. The hybrid rechargeable energy storagedevice of claim 1, wherein said electrolyte comprises a non-aqueouselectrolyte selected from organic solvents, polymer gels, polymers,ionic liquids, and ion-conductive solids.
 19. The hybrid rechargeableenergy storage device of claim 18, wherein said organic solventcomprises at least one of ethylene carbonate, diethyl carbonate,propylene carbonate, and acetonitrile.
 20. The hybrid rechargeableenergy storage device of claim 18, wherein said ion-conductive solidcomprises lithium titanium phosphate and materials occupyingperovskite-, NASICON- and Li₄SiO₄-type crystal structures.
 21. A hybridrechargeable energy storage device comprising: a positive air electrodecomprising at least one catalyst for oxygen reduction and evolution; anegative capacitive electrode comprising a double layer electrochemicalcapacitor comprising at least an electro-active material consisting of acomposite or compound; an ion permeable separator; and a non-aqueouselectrolyte containing metal ions, wherein the negative capacitiveelectrode comprises at least one material selected from electro-inertmaterials, said at least one material is configured to provide anon-faradic reaction, and wherein a capacitive electrode processcomprises a non-faradic reaction which contributes to the overallspecific capacitance of said capacitive electrode.
 22. The hybridrechargeable energy storage device of claim 21, wherein said capacitivematerial comprises a composite containing a carbonaceous material and amaterial selected from semimetals and metals that do not dissolve duringdischarging.
 23. The hybrid rechargeable energy storage device of claim21, wherein said capacitive material comprises a compound selected frommetal oxides, metal sulfides, metal selenides, metal phosphides, metalborates, metal nitrides, and their mixtures.
 24. The hybrid rechargeableenergy storage device of claim 21, wherein said at least one material isselected from electro-inert materials comprising: activated carbons,porous carbons, carbon foams, carbon fibers, carbon nanotubes, graphene,and carbon nanoparticles, which is configured to provide a non-faradicreaction.